Discovery leaves space station for the last time (Update)

In this March 4, 2011 photo provided by NASA, inside the newly installed Permanent Multipurpose Module (PMM) on the International Space Station are the six crew members of the STS-133 crew who've been spending busy days with the six astronauts and cosmonauts of Expedition 26, not shown. At bottom, from the left, are astronauts Eric Boe, Steve Lindsay and Michael Barratt. On top are astronauts Alvin Drew, Nicole Stott and Steve Bowen (AP Photo/NASA)

Discovery, the world's most traveled spaceship, left the International Space Station on Monday for the last time, getting a dramatic send-off by the dozen orbiting astronauts as well as "Star Trek's" original Capt. Kirk.

Station skipper Scott Kelly rang his ship's bell in true naval tradition, as the shuttle backed away on the final leg of its final journey.

"Discovery departing," he called out.

Discovery is due back on Earth on Wednesday. It's being retired after touchdown and sent to the Smithsonian Institution for display. NASA's two other shuttles will join Discovery in retirement, following their upcoming missions.

Discovery's astronauts got a special greeting in advance of their space station departure.

Actor William Shatner, who played Capt. James Kirk on the original "Star Trek" TV series, paid tribute to Discovery's voyages over the decades.

"Space, the final frontier," Shatner said in a prerecorded message. "These have been the voyages of the space shuttle Discovery. Her 30-year mission: to seek out new science, to build new outposts, to bring nations together on the final frontier, to boldly go and do what no spacecraft has done before."

Shatner's words were followed by Monday morning's wake-up music, "Theme from Star Trek." It was the runner-up in a pick-the-wake-up-music contest sponsored by NASA. The No. 1 vote-getter will be beamed up Tuesday.

Discovery will have racked up nearly 150 million miles by trip's end, accumulated over 39 missions and nearly 27 years, and spent 365 days total in space. It flew to the space station 13 times.

Immediately after undocking high above the Pacific, Discovery performed a victory lap around the orbiting outpost, where it spent the past nine days. The two crews beamed down pictures of each other's vessel, with the blue cloud-specked planet 220 miles below as the backdrop.

Close-up shots showed most, if not all, of the individual compartments of the bigger-than-ever station. Live NASA TV footage showed Discovery as it flew over the Atlantic and the Sahara, and in a matter of a few minutes, over the Mediterranean and northern Italy.

"It looks beautiful," Kelly said of Discovery. He wished the six shuttle passengers a safe ride home.

The two crews paid their own special tribute to Discovery, NASA's oldest surviving shuttle, during a joint farewell ceremony Sunday.

Discovery and its crew delivered a new storage compartment, as well as an equipment platform and the first humanoid robot in space. Both of the large items were successfully installed, and the shuttle astronauts even did some extra chores during their two extra days at the station. It ended up being a 13-day mission for Discovery.

R2 the robot, short for Robonaut 2, has yet to be unpacked. The space station residents hope to get to it in the next week or two.

The addition of the 21-foot-long, 15-foot wide storage compartment left the space station 97 percent complete. The complex now has a mass of nearly 1 million pounds.

On the next shuttle flight, by Endeavour next month, a huge science experiment will be installed on the outside of the space station, wrapping up the U.S. contributions. Atlantis will blast off with supplies on the final shuttle mission at the end of June.

NASA is under presidential direction to focus more on outer space, beginning with expeditions to asteroids and then Mars.

American astronauts, meanwhile, will continue hitching rides to the space station on Russian Soyuz spacecraft, at great expense. The intent is for private U.S. companies to take over those ferry operations within a few years.

Mission Control, meanwhile, monitored a piece of space junk - an old rocket part - that possibly was going to stray too close to the space station on Wednesday. Experts wanted to wait until after the shuttle's undocking, before deciding whether the complex needed to move out of harm's way. But it was looking less likely that it would pose a concern, officials said Monday.